Studies On New Types Of Highly Efficient Tandem And Hybrid Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSC) is a new type of photovoltaic cell, which simulates the natural photosynthesis principle. It has attracted much attention due to its high theoretical efficiency, low cost, and simple fabrication technique. The theoretical energy conversion efficiency of DSC is 33-36%, however, the actual efficiency of 11～13% is achieved in laboratory. Extensive efforts have been carried out on the further improvement of the energy conversion efficiency of DSC. One of the effective methods is broadening the absorption spectra and improving the harvest of light. Tandem DSC and hybrid DSC have attracted much attention due to their novel structure and particular characteristics. These structures not only can avoid the unfavorable competitive adsorption and interactions between dyes, but also can achieve the high open circuit voltage (VOC) and the short circuit current density (JSC)-The traditional structures of DSCs and the low efficiency of NIR dyes restrict the improvement of the efficiencies of tandem DSCs. So far, there are few reports on the hybrid DSC. In addition, the low efficiency, complex process, and rigorous fabrication condition restrict the application. On the other hand, the problems of NIR dyes currently used for DSCs are the low efficiencies owing to the narrow absorption bands and insufficient utilization of NIR light. Therefore, it is necessary to develop new NIR dyes with strong and broad absorptions. This research focus on the design and investigation on the new types of highly efficient tandem DSCs and hybrid DSCs, as well as developing NIR dyes with strong and broad absorptions for DSCs.Firstly, three types of tandem DSCs were designed and fabricated, with the structures of four-electrode-crossed type, four-electrode-back to back type and three-electrode-face to face type. The superposition character of tandem DSCs and the influencing factors of the efficiencies of top and bottom cells in different structures were systematically studied. The superposition of Jsc and efficiency were obtained. We also found that the efficiency of the top cell was affected by the photoanode and the counter electrode. The transmittance of the different structured tandem DSC, the photoanode of the top cell, as well as the counter electrode determined the efficiency of the bottom cell. The efficiency of tandem DSC was about the sum of the values of top and bottom cells. Secondly, we designed and fabricated a new type of DSC with a hybrid photoanode. A film-transfer technique was also developed. The high efficiency and the validity of the structure were systematically investigated, as well as the interactions between dyes and the mechanism on VOC The results showed that the hybrid structure can effectively broaden the absorption spectra and achieve a panchromatic response. The superposition of IPCE and Jsc were confirmed. A high efficiency of 11.05% was achieved. The high FOC of hybrid DSC and the back reactions at the TiO2/dye/electrolyte interface were analyzed by investigating on the photoelectrochemical properties. We compared the performances of the hybrid DSC with those of tandem DSC and co-sensitized DSCs, and the highest efficiency of hybrid DSC was achieved. The absorption spectrum was effectively broadened and the efficiency was significantly improved with the developed new type of hybrid DSC.Finally, four kinds of nickel bis(dithiolene) complexes with different groups were designed and synthesized. The physical and chemical properties were systematically investigated, including structure, electrochemical and photochemical behavior, etc. The results revealed the good thermal stability of the complexes. Strong and broad absorptions in the NIR region (700-1100 nm) with high molar extinction coefficients of the complexes were observed. Both the substituent effect and solvent effect can affect theλmax of the complexes. The spectroelectrochemical properties indicated the generation of different species under the bias. The electrochemical results showed the good reversibility of the complexes. The energy levels, as well as the electron distribution of the dyes were computed by Density Functional Theory (DFT) calculations. These NIR dyes were used for DSC and the feasibility was confirmed.